Using Mergesort to calculate number of inversions in C++
- by Brown
void MergeSort(int A[], int n, int B[], int C[])
{
if(n > 1)
{
Copy(A,0,floor(n/2),B,0,floor(n/2));
Copy(A,floor(n/2),n-1,C,0,floor(n/2)-1);
MergeSort(B,floor(n/2),B,C);
MergeSort(C,floor(n/2),B,C);
Merge(A,B,0,floor(n/2),C,0,floor(n/2)-1);
}
};
void Copy(int A[], int startIndexA, int endIndexA, int B[], int startIndexB, int endIndexB)
{
while(startIndexA < endIndexA && startIndexB < endIndexB)
{
B[startIndexB]=A[startIndexA];
startIndexA++;
startIndexB++;
}
};
void Merge(int A[], int B[],int leftp, int rightp, int C[], int leftq, int rightq)
//Here each sub array (B and C) have both left and right indices variables (B is an array with p elements and C is an element with q elements)
{ int i=0;
int j=0;
int k=0;
while(i < rightp && j < rightq)
{
if(B[i] <=C[j])
{
A[k]=B[i];
i++;
}
else
{
A[k]=C[j];
j++;
inversions+=(rightp-leftp); //when placing an element from the right array, the number of inversions is the number of elements still in the left sub array.
}
k++;
}
if(i=rightp)
Copy(A,k,rightp+rightq,C,j,rightq);
else
Copy(A,k,rightp+rightq,B,i,rightp);
}
I am specifically confused on the effect of the second 'B' and 'C' arguments in the MergeSort calls. I need them in there so I have access to them for Copy and and Merge, but
